Continuously modulated electrode boiler

ABSTRACT

An electrode boiler apparatus for converting electrical energy to heat energy includes an electrically conductive container or pressure vessel containing an electrically conductive liquid in which is immersed at least one pair of electrodes. A variable reactance is mounted upon the container and connected to a power source to induce current into the container walls. The electrodes are mounted for movement relative to each other to vary the effective current path between the electrodes and the electrodes are connected in series with the variable reactance. Adjustment of the spacing between the electrodes provides continuous power control from full load down to 5-15 percent of the full load rating, at which point the inductive reactance of the variable reactance increases to reduce the power drawn to a no load condition. The variable reactance may comprise a saturable laminated C-shaped core mounted on the container wall and provided with a coil wound about the core and connected in series with the electrodes. Alternatively, the variable reactance may comprise a saturable reactor.

[ Feb 4, 1975 Primary Examiner-A. Bartis Attorney, Agent, or Firm-DorseyL. Baker [57] ABSTRACT An electrode boiler apparatus for convertingelectrical energy to heat energy includes an electrically conductivecontainer or pressure vessel containing an electrically conductiveliquid in which is immersed at least one pair of electrodes. A variablereactance is mounted upon the container and connected to a power sourceto induce current into the container walls.,The electrodes are mountedfor movement relative to each other to vary the effective current pathbetween the electrodes and the electrodes are connected in series withthe variable reactance. Adjustment of the spacing between the electrodesprovides continuous power control from full load down to 515CONTINUOUSLY MODULATED ELECTRODE BOILER Inventor: Glenn R. Mohr,Linthicum, Md.

Assignee: Mohr-Baker C0., West Chicago, 111.

[22] Filed: May 29, 1973 Appl. No.: 364,679

219/285, 13/5, 219/1047, 219/1049, 219/272, 219/289, 219/503 Int. 1105!)3/60, l-l05b 1/02 Field of Search 219/284295,219/271276,503,1049,1051,10.47, 10.65, 10.75, 10.77, 327; 13/5References Cited UNITED STATES PATENTS llnited States Patent M011! 5395.5 3 9 3 25 3 ww w A w llwlwfiflfimo S 2 2 2 9999 2 ,.2 llllw m. N.22221 m w nuaununnvnz n A "Nu" n C m nun U 1.1.. ."mmm M M "N "MUN an naur u u u H u A u mac. n lu i nnuu H n R n Mac l "t." a u mK M l OH W F8 006 M .bZ S Z L n UHHH T me ..1 Me W HHLMKWHHJW ES, T 47005070905 A20112334466 2 9999999999 9 llllllllll N l 3920300035 ll 1 l l E 407000206 6 59 447539oo O3 4524 nw5 7 5 5 6 4999060559 2 538559 63 9 722 5 7o 7w4 9 7w 111122223 PATENIEU 4W5 3.864.543

sum 1 or 2 KVA KVA CONTINUOUSLYMODULATED ELECTRODE BOILER BACKGROUND OFTHE INVENTION This invention relates to'a system and apparatus forconverting electrical energy into heat energy. More specifically, itrelates primarily to a system and apparatus for heating water'and otherliquids to meet the needs of commercial buildings or industrialfacilities. Such needs may relate to the usage of the fluid or the merestorage of heat energyfor subsequent use.

Currently available electrical heating systems require switchgear toswitch the system on and off the line as dictated by the temperature ofthe liquid or other control parameters. Additionally, they needprotective devices which limit the maximum current which can be drawn.Finally, available systems have limited control ranges and do not permitthe desired modulation by the system.

An optimum electrical heating system would have the following desirablefeatures:

I. A large turn down ratio, exceeding 30:];

2. A capability to remain on the line at all times regardless of thecontrol parameters, thus eliminating the need for switch gear;

3. Continuous modulation from a no load to a full load condition;

4. A high power factor;

5. A minimum number of components, elimination of contactors and switchgear;

6. A current limiting capability;

7. An ability to vary both current and voltage within the boilertoobtain the large turn down ratio.

Finally, other considerations require that a heating system have a goodwave form to prevent radiation and interference with-instrumentation andtelevision reception, be of relatively low cost with simplicity ofdesign.

SUMMARY OF THE INVENTION In order to obtain these desirable features,the instant invention includes a container having a variable .resistancethrough which the electrical energy is converted to heat energyQtheresistance being in series with a vari-' able reactance. By varying theresistance, the power drawn and converted to heat energy is modulatedfrom full load to approximately to percent of the full load rating.Below this level, the inductive reactance of the variable reactancereduces the power drawn to a no load condition which limits the power toa minimum core magnetizing level. Preferably, the variable resistancetakes the form of at least one pair of relatively moveable electrodeswhile the reactance takes the form of a C-shaped core mounted or weldedto the container and a coil wound about the core which is connected toone of the electrodes.

Accordingly, it is an object 'of the instant invention to my inventionto obtain all of the desirable features of an electric boiler previouslymentioned.

DESCRIPTION OF THE DRAWINGS The manner in which these and other objectsof the invention can be obtained can be better understood power drawn asa function of the resistance and inductive reactance;

FIG. 4 is a graph illustrating the variation of the power drawn as afunction of the total impedance;

FIG. 5 is a side elevational view in section of a preferred imbodimentof my invention;

FIG. 6 is a plan view taken in section along the lines 55 of FIG. 5;

FIG. 7 is an enlarged side elevational view of the variable reactor ofmy invention; and

FIG. 8 is a diagram of another preferred embodiment of the electricalcircuit of my invention.

DETAIL DESCRIPTION In order to obtain the aforementioned objects, theinstant invention modulates the power delivered to an electric boiler bythe use of a variable reactance in series with a variable resistance.The resistance comprises relatively movable electrodes. The variablereactancemay comprise a saturablelaminated core with a winding thereonconnected in series with the resistance. At high power levels, theelectrodes are adjacent one another to minimize resistance and theinductive reactance is very small to provide a good power factor.Continuous modulation down to a desired power level (5 15 percent offull load rating) is accomplished by increasing the effective currentpath between the electrodes. As the current drawn decreases below thesaturation point of the core, the reactance increases. Thus with R and Xboth increasing, the high impedance reduces the current drawn to a noload condition.

The electricalcircuit of the preferred embodiment of my invention isbest described in'FIG. 1. The circuit 50 preferably includes threevariable reactances 60 which are adapted for connection to a three phasepower supply as indicated in FIG. 1. These variable reactances take theform of a C-shaped laminated core welded to the walls of the boilerhaving windings connected to the power source. Preferably, the core isdesigned (as subsequently explained) so as to saturate when the boiler.is drawing between 5 and I5 percent of the full load rating of theboiler. Connected in series with each reactor is a variable resistance80. These resistances preferably take the form of three pairs of wyeconnected electrode sets mounted within a container (as subsequentlyexplained) for-relative movement to vary the effective current pathbetween them.

FIGS. 5 7 depict the preferred embodiment by directs cold liquids to thecontainer while outlet 30 provides heated liquids to the user upondemand.

Each of the three variable reactances 60 may take the form of laminatedC-shaped sections 62 mounted by welding or other means to the containerwall 22. A winding 64 preferably of copper or aluminum is wound aboutthe core as shown in these figures and is adapted to be connected to athree phase source. As shown in FIG. 7, the container wall 22 inconjunction with the sections 62 form a closed core. The complete core,

e.g., the C shaped sections 62 and the container wall 22 should bedesigned so as to saturate at a power level between 5 and percent of thefull load rating of the unit.

With. specific reference to FIG. 7, a preferred embodiment of myreactance'60 includes one leg (e.g., the container wall 22) which has asmaller cross section than laminated sections 62. It is this smallercross section which should be designed to saturate at approximatelya 15percent power level and which functions as an induction heater(subsequently explained).

Each winding 64 is then. connected to the variable resistances 80 whichcomprise pairs of sets of electrodes 82, and 92. The first set 82 ofeach pair is carried within the tank by insulators 84 which compriseupstanding arcs of electrical insulators carried by fixed supportsmounted on opposing are shaped insulating units 94.

These units are rotatably carried upon a shaft 32 which is journaled inthe top and bottom of the tank as shown for rotation 'by a motor M.Again, these electrodes are interconnected by a common conduit which isgrounded after being connected to the rotable shaft 32. As shown in fulllines, the boiler is in the full load position. I

The motor M and shaft 32 should be designed to rotate the second sets ofelectrodes 92 and their insulating units through an arc of approximately60 which is shown in the .dotted line position of FIG. 6. In thisposition, these movable electrode sets are adjacent addi- 4 tance X isalso small andtheunit can draw its full rated load. Thus, maximum KVA isdrawn while X,,, R

and total impedance are a minimum as shown in FIGS.

3 and 4. Further, beyond saturation, the current drawn and ampere turnsof the windings increases substantially. Therefore the magnetomotiveforce or field intensity through the wall section 22 increases to inducea voltage therein which inturn creates substantial eddy currents totransform the wall from a-mere container to an induction heater.

'As the temperature of the liquid rises, the control unit (not shown)will sense the temperature and actuate the motor to rotatethe'electrodes towards the dot ted line position. Such will cause theresistance to increase and' hence the voltage across the electrodes mustincrease. Consequently the voltage across the reactor 60 will decreasebecause the applied voltage is still constant. When the resistanceincreases sufficiently, the voltage drop (IX across the reactance 60will be below thelevel necessary to maintain saturation. Belowsaturation, the reluctance of the core detional insulating units 106which may be identical to the otherunits but have no electrodes therein.When rotated to this position, the electrodes 92 are shielded from theelectrodes 82. Too, the top and bottom flanges 88 as well as flanges 90at each side preclude sents the no load position.

MODE OF OPERATION Assuming that the temperature of liquid in thecontainer is to be raised, a control unit (not shown) which sensestemperature will actuate the motor M to rotate the electrode sets 92 tothe full line position of FIG. 6 such that the variable resistances 80or effective current path between the pairs of electrode sets 82 and 92is at a minimum. Considering the voltage equation E IR IX the value of Ris small in this position and does not inhibit current flow. Too,because the wall section 22 was saturated at a 15 percent power level,its permeability decreases and reluctance increases causing the flux perampere to decrease; This is represented in FIG. 2 by a small change influx compared to a large change in current. Hence, the inductivereaccreases andfor the same amount of magnetomotive force, the inductivereactance increases rapidly. The graphs of FIGS. 2.3 and 4 are merelyillustrative and are not intended'to represent actual quantative values.However, it should be observed that the modulation of the power drawn bymy invention is continuous from the full load condition down to the 15percent level. The modulation below the 15 percent level is representedby a second curve (indicated at b) which is also continuous.

At this point it should be noted that losses due to hysteresis representusable power. Since the tank is part of the cores, the heat generated"will be delivered to-the fluid. Obviously, the C-shaped cores might alsobe placed horizontal to the ground or at to the position shown in FIGS.6 and 7. Such would cause the flux to flow around the tank for moreuniform heating of the wall section.

ment is depicted in full lines in FIG.'4. Such is continuous from thefull load rating down to the saturation point (5-. 15 percent powerlevel) of the load. How-.

ever, it may bedesirable to continuously modulate the power drawn downto the no load condition as indicated by the dotted curve. This can beeasily accomplished by the use of the circuit of FIG. 8 in whichsaturablereactors are placed in series with the resistances 80. However,in this case two reactors are used with each pair of electrodes. The ACwindings of each reactor are connected in either parallel or in serieswith each other and both windings are in series with the electrodes.Wound about the same cores or an additional leg of each core are DCwindings whichcontrol the amount of flux in the core. As the DC voltageis reduced, the flux decreases causing the reactance to increase as afunction of the applied DC This invention may take many other forms. Forexample, the electrodes may be moved vertical relative to one another orshielding may be used to provide effective relative .movement. Too, theelectrodes may be of carbon or which has substantial utility without theuse of electrodes. For example, the windings may be connected to thesource and to a return line to obtain an inexpensive, external heater.ln this case, the heating element (wall section 22) is external,visually observable and requires no maintenance. Silicon controlledrectifiers (SCR) or saturable reactors are used to control the currentflow through the windings, and the electrodes or internal heating unitsare eliminated. Finally, this heating system will find application as aninduct heater for forced air ducts and similar uses.

I claim:

1. An electrode boiler comprising:

A. An electrically conductive container means;

B. A pair of relatively movable electrodes within said container meansfor creating a current path through a fluid within said container means;

C. A variable reactance adapted to be connected to a power source and inseries with the movable electrodes. said reactance being mounted uponsaid container and including an inductance means for passing fluxthrough the container means to induce a current therein.

2. A device as recited in claim 1 in which:

A. Said variable reactance comprises a saturable reactor.

3. A device as recited in claim 1 in which:

A. Said variable reactance comprises a wall of the container means and aC-shaped core mounted thereon and carrying a winding adapted to beconnected to the power source and the electrodes.

4. A boiler comprising:

A. An electrically conductive'container structure;

B. Variable resistance means within said container for convertingelectrical energy to heat energy and for modulating the power drawn;

C. A variable reactance means mounted upon said container structure inseries with said resistance means and adapted to be connected to a powersource for further modulatingthe power drawn and for inducing current insaid container structure.

5. An apparatus as recited in claim 4 in which:

A. The variable resistance means modulates the power from the rated loadof the boiler down to about 10 percent of the rated load; and

B. The reactance means and resistance means modulates the power drawnfrom about 10 percent of the rated load down to the no load condition.

6. An apparatus as recited in claim 4 in which:

A. Said resistance means comprises three pairs of electrode units wyeconnected;

B. Said reactance means comprises three variable reactors adapted to beconnected to a three phase power source and in series with saidelectrode units.

7. An electrode boiler comprising:

A. An electrically conductive container structure having a fluid inletand outlet;

B. A variable reactance adapted to beconnected to a source'of electricalenergy and mounted upon said container structure and for inducingcurrent therein;

C. A variable resistance within said container, connected in seriesto'said variable reactance and to a return conduit for varying thereactance for varying the energy drawn and converted to heat;

D. Means for varying the reactance for varying the energy drawn andconverted to heat.

8. A device as recited in claim 7 in which:

A. Said resistance comprises at least one pair of relatively movableelectrodes for varying the effective current path therebetween.

9. A device as recited in claim 8 in which:

A. Said variable reactance comprises a core and winding mounted upon thecontainer.

10. A device as recited in claim 9 in which:

A. Said core comprises a section of the container wall and a C shapedlamination mounted thereon.

11. A device recited in claim 7 in which:

A. Said variable reactance comprises a saturable reactor.

1. An electrode boiler comprising: A. An electrically conductive containEr means; B. A pair of relatively movable electrodes within said container means for creating a current path through a fluid within said container means; C. A variable reactance adapted to be connected to a power source and in series with the movable electrodes, said reactance being mounted upon said container and including an inductance means for passing flux through the container means to induce a current therein.
 2. A device as recited in claim 1 in which: A. Said variable reactance comprises a saturable reactor.
 3. A device as recited in claim 1 in which: A. Said variable reactance comprises a wall of the container means and a C-shaped core mounted thereon and carrying a winding adapted to be connected to the power source and the electrodes.
 4. A boiler comprising: A. An electrically conductive container structure; B. Variable resistance means within said container for converting electrical energy to heat energy and for modulating the power drawn; C. A variable reactance means mounted upon said container structure in series with said resistance means and adapted to be connected to a power source for further modulating the power drawn and for inducing current in said container structure.
 5. An apparatus as recited in claim 4 in which: A. The variable resistance means modulates the power from the rated load of the boiler down to about 10 percent of the rated load; and B. The reactance means and resistance means modulates the power drawn from about 10 percent of the rated load down to the no load condition.
 6. An apparatus as recited in claim 4 in which: A. Said resistance means comprises three pairs of electrode units wye connected; B. Said reactance means comprises three variable reactors adapted to be connected to a three phase power source and in series with said electrode units.
 7. An electrode boiler comprising: A. An electrically conductive container structure having a fluid inlet and outlet; B. A variable reactance adapted to be connected to a source of electrical energy and mounted upon said container structure and for inducing current therein; C. A variable resistance within said container, connected in series to said variable reactance and to a return conduit for varying the reactance for varying the energy drawn and converted to heat; D. Means for varying the reactance for varying the energy drawn and converted to heat.
 8. A device as recited in claim 7 in which: A. Said resistance comprises at least one pair of relatively movable electrodes for varying the effective current path therebetween.
 9. A device as recited in claim 8 in which: A. Said variable reactance comprises a core and winding mounted upon the container.
 10. A device as recited in claim 9 in which: A. Said core comprises a section of the container wall and a C shaped lamination mounted thereon.
 11. A device recited in claim 7 in which: A. Said variable reactance comprises a saturable reactor. 